In certain countries, environmental laws require that exhaust emission reduction equipment such as aftertreatment devices be continuously monitored by on-board diagnostic (OBD) systems.
Aftertreatment devices are well known and widely used in various internal combustion engine applications for the aftertreatment of engine exhaust gases. Devices such as selective catalytic reduction (SCR) catalyst devices have been useful for handling and/or removing nitric oxide in the exhaust stream of an engine.
The SCR catalyst devices typically utilize a catalytic reducing agent. The exhaust gas reacts with a reagent solution on the SCR catalyst device so as to reduce the nitric oxide content in the exhaust gas stream.
In some OBD methods involving the monitor of a SCR catalyst device, kinetics of temperature changing across the catalyst are measured to detect catalyst device absence, reverse and damage. However, such methods take exhaust mass flow, which significantly affects temperature of the changing kinetics, as an uncertainty. As a result, a tradeoff between high false alarm rates and high false passing exists.
In other known OBD methods, exhaust temperatures at engine cold start are used as a base line. These methods however can only be applied after the engine is cooled to ambient temperature.
Thus, there is a need to provide an improved OBD method that can monitor catalyst device integrity more accurately and is not limited by the status of the engine.